I. Field of the Invention
The present invention relates generally to an information recording method. More specifically, the invention relates to a method for recording information on a disc which has a recording layer capable of changing to a crystal condition and to an amorphous condition reversibly.
II. Description of the Related Art
With the wide-spread use of multimedia products, read only media such as audio CD and CD-ROM media, as well as the optical information reproducing apparatus used to record and reproduce such discs have been widely used. Due to the desire of users to create their own customized media, write-once discs using a dye technique (commonly known as CD burning), magnetic optical discs (MO) and phase-change discs have also received great attention within the field.
With the advent of reducing the amplitude of the laser diode, minimizing the spot diameter by using a high numerical aperture (NA) objective lens and adopting a thin substrate, high capacity optical discs such as the DVD-ROM, DVD-R, DVD-RAM, DVD-RW have been made possible. Currently, the major focus is erasable DVD media, which will be the next step for recording multi-media with great storage capacity. However, phase-change discs can also provide the functionality of an erasable DVD in a more efficient manner.
In a phase-change disc, information is recorded by changing a recording layer into a crystal condition or an amorphous condition reversibly. It can record and reproduce information only by laser ray from the laser diode. However, it does not require an external magnet, as with MO discs. Furthermore, a phase-change disc is capable of xe2x80x9coverwrite recording,xe2x80x9d which is the recording and erasing of information at the same time.
For example, a single pulse light waveform of the laser diode using the EFM (Eight Fourteen Modulation) pulse code modulation is used as a general recording waveform for recording information on such phase-change discs. However, in such a single pulse recording method, recording marks are crooked in the form of tears because of the regenerative action and insufficient amorphous phase formation, which falls short of the appropriate cooling speed. Therefore, recording marks with low reflective rates cannot be obtained.
As a conventional recording method for recording information on a phase-change disc, the recording marks are formed by the laser ray of a multi-pulse waveform with some recording power steps reproduced based on a recording rate such as 8-16 pulse code modulation, as shown in FIG. 1. This known practice solves the above problem.
Marked portions of the multi-pulse waveform comprise a head heating pulse xe2x80x9cAxe2x80x9d for preheating the recording layer of the phase-change disc until the melting point degree is exceeded, followed by plural serial heating pulses xe2x80x9cB,xe2x80x9d and serial cooling pulses xe2x80x9cCxe2x80x9d between pulses xe2x80x9cAxe2x80x9d and xe2x80x9cB.xe2x80x9d When the intensity of the head heating pulse A is Pwa, the intensity of the serial heating pulse B is Pwb, and the intensity of the serial cooling pulse C is Pwc. The result is the reproduction of the intensity Pr. Each intensity is set to the following expression.
Pwbxe2x89xa7Pwa greater than Pwc=Pr
Space portions of the multi-pulse waveform comprise an erase pulse D. When the intensity of the erase pulse D is Ped, the intensity is set to the following expression.
Pwa greater than Ped greater than Pwc
Based upon those expressions, the marked portions are formed into an amorphous phase, which is based on the rapid cooling conditions among the heating pulses A, B and the cooling pulse C. The space portions are formed into a crystal phase based on the gradual cooling condition induced solely by heating. Therefore, the reflective rate difference between the amorphous phase and the crystal phase is fully obtained.
A mark position recording method (PPM) and a mark edge recording method (PWM) are used to record information on phase-change discs. Currently, the mark edge recording method is used in response to high density recordings. Since phase-change discs have information at both edges of the recording marks, when recording information on the phase-change discs by the mark edge recording method it is important that sufficient heating and rapid cooling are carried out on the disc and that the edges of the marks are formed clearly. Therefore, high recording power is desired which may be achieved by changing the angle of the disc and increasing the light power of the laser diode. With recent high density recording, it is possible to form minute marks on the disc by using a short wavelength laser and a high NA objective lens. However, in conventional basic recording, when the effective spot diameter of the recording spot and the shortest mark length, which are formed on the disc by the laser ray, are close to each other the shortest mark becomes long. Therefore, it is advantageous to configure a system such that the erase power is high and the edge of the marks are short.
As a point of reference, in the early days of CD-ROM or DVD-ROM technology, the Constant Linear Velocity (CLV) method, which increased recording capacity, was generally used as the speed control method for the spindle motor. However, when the rotating speed of the spindle motor is increased, for the purpose of significantly increasing the information transmission speed, the rotating angle speed has to be constant for the purpose of simplifying the motor control.
Another method, the Constant Angular Velocity (CAV) method, has a constant rotating angular velocity and a constant recording frequency. When using the CAV method, the linear speed on the disc for the laser ray is high and information recording density is low. This method records by moving the laser ray from the inner area to the outer area of the disc. The zone CAV method, commonly referred to as the ZCAV method, divides the disc surface into concentric circles, then records and reproduces using a constant frequency in each zone. The further the zone is to the outer edge, the higher the frequency. This method provides greater recording capacity, while the recording linear density does not change significantly among the zones.
When recording by the CAV and the ZCAV methods, as the laser moves from the inner area to tie outer area of a disc, the linear speed on the disc with reference to the laser ray is high. Therefore, the circuit design can be complicated because measures must be taken into account for the reduced power of the laser or the raise in the channel clock frequency. When recording information on a disc according to the CLV recording method, if the linear speed is too high or too low, the resulting recording may be unsatisfactory because such a linear speed condition causes a deterioration in the overwriting and increases the jitter on the disc.
For the purpose of resolving such a problem, for example, in an information recording method shown in Japanese unexamined patent publish (KOKAI) No 06-12674, when the relative speed between a recording disc and a laser ray is high, a pulse being a little shorter than an input pulse is radiated. However, such a pulse is not a multi-pulse. In an information recording method shown in Japanese unexamined patent publish (KOKAI) No 05-274678, the duty rate of the light pulse when radiating a laser ray in the outer area is greater than when radiating a laser ray in the inner area.
In the above-mentioned information recording method, the light pulse must be changed according to the radial position of the laser ray from the disc""s center. This results in a complicated circuit structure for the laser radiating control unit. However, there is a conventional method which makes the multi-pulse width constant in view of time, regardless of the change in linear speed. In such a method, the higher the linear speed and the channel clock frequency, the higher the radiating rate of the multi-pulse is for the channel clock.
However, when recording information on the outer area or the inner area of the optical disc, where the multi-pulse width is constant in view of time, such conditions are not always suitable and may result in the overwriting and the jitter worsening.
It is therefore an object of the present invention to provided an information recording method, using CAV or zone CAV control, which improves the overwriting and jitter. Such a method provides for a rear heating pulse width in a multi-pulse line which is constant in view of time, regardless of the recording linear speed of a recording medium.
In accordance with the structure of the present invention, an information recording method forms marks or spaces based a predetermined recording modulating method, such as 8-16 pulse code modulation, on a recording medium. It does so by radiating a light source using a multi-pulse line, which includes a head heating pulse and a head cooling pulse, followed by plural serial rear heating pulses and serial rear cooling pulses. The width of the rear heating pulses are constant in a view of time, regardless of the recording linear speed of the recording medium. When recording information having pulses N times as long as the channel clock cycle T, by the laser ray from a laser source (where Nxe2x89xa71), the recording method uses a CAV control which utilizes a constant recording frequency and a constant rotating angular velocity or zone CAV control. The constant rotating angular velocity or zone CAV control raises the recording frequency as the laser ray moves from the outer area and out of each zone. Each zone is divided into concentric circles on the disc. There, the recording medium has a recording layer changing into a crystal condition and an amorphous condition reversibly.
In accordance with the first structure of the present invention, the information recording method is set such that the width of the head heating pulse remains at a constant rate for the channel clock cycle T.
In accordance with the second structure of the present invention, the information recording method is characterized by configuring the rate for the channel clock cycle T by changing the head heating pulse based upon the recording linear speed of the recording medium and the recording density of is the recording medium.
In accordance with the third structure of the present invention, the information recording method is characterized by setting the pulse number of the multi-pulse line and the width of the last cooling pulse change based upon a change in the recording density of the recording medium.
In accordance with the fourth structure of the present invention, the information recording method sets the rate for the channel clock cycle T of the head heating pulse width to be large, and sets the rate for the channel clock cycle T of the last cooling pulse width to be small. This condition is used in the area where the recording linear speed of the recording medium is lower than the center linear speed of the linear speed change and where the recording density is high.
In accordance with the fifth structure of the present invention, the information recording method is characterized by setting the rate for the channel clock cycle T of the head heating pulse width to be large, and making the rate for the channel clock cycle T of the last cooling pulse width to be small. This condition is used in the area where the recording linear speed of the recording medium is higher than the center linear speed of the linear speed change and the recording density is low.
In accordance with the sixth structure of the present invention, the information recording method is characterized by setting the rate for the channel clock cycle T of the head heating pulse width to be small, and making the rate for the channel clock cycle T of the last cooling pulse width to be large. This condition is used in the area where the recording linear speed of the recording medium is lower than the center linear speed of the linear speed change and the recording density is low.
In accordance with the seventh structure of the present invention, the information recording method is characterized by setting the pulse number of the multi-pulse line xe2x80x9cNxe2x88x922xe2x80x9d, and setting the rate for the channel clock cycle T of the last cooling pulse width to be large. This condition is used in the area where the recording linear speed of the recording medium is higher than the center linear speed of the linear speed change and the recording density is high.
In accordance with the eighth structure of the present invention, the information recording method includes suitable linear speed for recording. Moreover, the middle value of the linear speed width is set to change in response to the CAV control or zone CAV control in the above structure.
In accordance with the ninth structure of the present invention, the information recording method has a recording layer where the recording medium includes Agxe2x80x94Inxe2x80x94Sbxe2x80x94Te type recording material.
In the above first structure, it is possible to keep the overwriting quality and the jitter on the whole area of the recording disc in satisfactory condition.
In the above second structure, it is possible to prevent the head portion from having deficient power, while keeping the overwriting quality and jitter satisfactory, by changing the last cooling pulse width as illustrated above.
In the above third structure, data can be recorded in an ideal mark length by suitable laser power. It is possible to keep the overwriting quality and the jitter condition satisfactory by changing width of the last cooling pulse as illustrated above.
In the above fourth structure, based upon the above illustrated linear speed and recording density conditions, it is possible to keep the overwriting quality and the jitter on the whole area of the recording disc in satisfactory condition.
In the above fifth structure, based upon the above illustrated linear speed and recording density conditions, it is possible to keep the overwriting quality and the jitter on the whole area of the recording disc in satisfactory condition.
In the above sixth structure, based upon the above illustrated linear speed and recording density conditions, it is possible to keep the overwriting quality and the jitter on the whole area of the recording disc in satisfactory condition.
In the above seventh structure, based upon the above illustrated linear speed and recording density conditions, it is possible to keep the overwriting quality and the jitter on the whole area of the recording disc in satisfactory condition.
In the above eighth structure, even if the linear speed changes from the lowest speed to the highest speed, it is possible to keep the overwriting quality and the jitter on the whole area of the recording disc in satisfactory condition.
In the above ninth structure, the relation between the accumulated length from the head cooling pulse to the last cooling pulse and the mark length for the pulse illustrate a tendency for each to correspond to each other in a straight line, resulting in an easy to control mark length.